Well, it's not Nintendo that does it--after all, Game Freak makes the games. But yeah, in actuality a number of Pokemon seem to be based off of or influenced by various daikaiju. For instance, Beautifly and Dustox seem to draw some inspiration from Mothra and Battra; Hydreigon sure does make me think of Ghidorah (this is especially due to pose; compare: [link] to [link] ); Zigra might've initiated the idea for Garchomp ( [link] ); and Tyranitar is very Godzilla-like.